1. Field of Invention
The present invention relates generally to a wireless power transmitter and a wireless power receiver, which may use a wireless power transmission technology and a technology capable of rapidly charging a battery.
2. Description of the Related Art
Using wired power transmission technology, charging is made possible only when a charger and a device to be charged are directly connected with each other in a wired manner or are connected with each other by a contact point. Thus, in order to charge the device using such technology, it is necessary for a user to perform an operation of directly connecting the device and the charger. This may cause an inconvenience in accordance with the appearance of a variety of portable devices using a battery and may result in a decrease in the amount of use thereof. There may also be an inconvenience caused by the complex location of power cables for the respective devices. In order to address problems of such a wired charging method, wireless power transmission technology has been developed and various studies thereon have been conducted.
The wireless power transmission technology is a technology that transmits power without a direct line or a contact point between the charger and a device desired to be charged, and has been recently and widely applied even to Electric Vehicles (EV) as well as smart phones and tablet PCs. The wireless power transmission technology may be classified into inductive, capacitive, and resonance methods in accordance with the method. The respective methods have advantages and disadvantages in terms of implementation or efficiency, and the electromagnetic inductive method and the resonance method are standardized and take the lead in the technologies. A significant difference between the two methods is that the operating frequency is in a range of several hundred kHz in the electromagnetic inductive method and the operating frequency is in a range of several MHz in the resonance method. In the electromagnetic inductive method, charging is made possible with high efficiency in a short charging distance, and in the resonance method, a charging distance may be increased.
A conventional wireless charging system to which the above-described wireless power transmission technology is applied generally includes a power transmitter and a power receiver.
FIG. 9 is a block diagram of a conventional wireless charging system, according to the related art.
Referring to FIG. 9, a conventional power transmitter 910 includes a single-phase or three-phase Alternating Current (AC) power supply unit 911, an adapter 914 for generating power required by a power transmission unit 915 for wireless charging from the AC power supply unit 911, and the power transmission unit 915 for generating power as a signal in the form in which wireless power transmission is possible.
The adapter 914 includes an AC/DC converter unit 912 and a DC/DC converter unit 913 to which a Power Factor Correction (PFC) circuit is applied, and power factor correction among roles of the AD/DC converter unit 912 constituting the adapter 914 may be an important function in accordance with the capacity of the adapter 914. For example, an adapter having a capacity of 75 W or larger among adaptors for a notebook should have a PFC function. In a case in which the PFC function is not required, a PFC portion can be seen as an AC/DC converter that converts AC power into DC power.
A conventional power receiver 930 includes a power reception unit 931 for generating Direct Current (DC) power using the signal generated from the power transmission unit 915 of the power transmitter 910, a DC/DC converter unit 932 for generating power in the form suitable for a charger Integrated Circuit (IC) 933 for charging a battery 934, the charger IC 933, and the battery 934.
In the structure of the wireless charging system as shown in FIG. 9, each of the power conversion units (the AC/DC converter unit 912, the DC/DC converter unit 913, a power transmission unit 915, a power reception unit 931, a DC/DC converter unit 932, and the charger IC 933) has a different power conversion efficiency according to the design specifications, but has efficiency characteristics of approximately 80% or more.
FIG. 10 is a graph illustrating efficiency characteristics in accordance with an output current and an input voltage of a conventional DC/DC converter unit, according to the related art.
Referring to FIG. 10 a graph showing efficiency characteristics according to an output current and an input voltage of the DC/DC converter unit 913 is provided. The graph displays efficiency characteristics of approximately 80%. The wireless charging system of FIG. 9 is subjected to power conversion operations of a total of six power conversion units, and transmits power to the battery 934 from the AC power supply unit 911, by which the battery 934 can be charged. Thus, when it is assumed that the efficiency of each power conversion unit is 80%, about 26% of power is transmitted to the battery 934 when 100% of power is supplied from the AC power supply unit 911. Meanwhile, when the efficiency of each power conversion unit is 80%, a larger amount of power may be transmitted.
A conventional battery charging method which has been most widely used in charging a battery is a Constant Current-Constant Voltage (CC-CV) charging method. The CC-CV charging method is a method that initially performs constant current charging and then performs charging using a constant voltage in the future, and many studies on the CC-CV charging method have been conducted, so that the CC-CV charging method may be implemented using an IC which is commercially available. However, in the conventional CC-CV method, several hours are typically required for charging from a fully discharged state of a battery to a fully charged state thereof, which is inconvenient for users. Thus, in order to address the problem in the battery charge time, studies on a rapid charging technology capable of rapidly charging the battery have been conducted. In addition, there are demands for the development of a rapid charging technology, such as the development of rapid chargers, rapid charging batteries, etc., due to the capacity limit of the battery in consideration of the power consumption increase of devices using a battery and the ease of the movement thereof.
To this end, a rapid charging technology in which a charging current is configured in the form of a multi-step in an initial CC charging section in the conventional CC-CV charging method has been developed. This technology applies a boost charging method that performs charging for a predetermined time using a current larger than that in the existing CC charging method as an initial charging current value.
FIG. 11 is a graph illustrating a profile of a boost charging technology among conventional rapid charging technologies, according to the related art.
Referring to FIG. 11, a profile of the boost charging method among the conventional rapid charging technology is provided. The boost charging method has an advantage in that initial charging is performed using a current larger than a CC current value in the CC-CV charging and then charging is performed in the existing CC-CV method when reaching a predetermined condition, thereby reducing a charging time.
As described above, in the conventional rapid charging technology, it is possible to reduce the charging time compared to the CC-CV charging method, but safety problems such as the reduction in the battery life due to a large current charge, the occurrence of a defect of a battery during charging, and the like have been reported.
Important requirements in the wireless power transmission and the rapid charging technology are the efficiency of a charging system and the ease of implementation thereof. However, in the case of the conventional wireless charging system to which the wireless power transmission technology is applied, an existing commercial adaptor is adopted and a charger IC of a charger is used as is, and thereby there are problems such as an increase in the structural complexity and an increase in costs. In addition, in the case of the technology in which the charging current in the initial CC charging section is configured in the form of multi-step in the conventional CC-CV charging method among the rapid charging technologies, the charging current in the initial CC charging section is configured in the form of multi-step, and thereby there is a problem of the system efficiency lower than that in the wired power transmission technology. In addition, in the implementation of the system to which the conventional rapid charging technology is applied, the complexity in the implementation is increased. For example, the conventional boost charging technology has a problem of a substantial increase in the complexity of the system implementation compared to the CC-CV method.